Increases in terrorist threats has created a need to deploy high speed, high resolution, and more accurate threat screening devices in locations which are most likely targets of such violence, such as ports, airports, train stations, and government buildings. Screening technologies currently employed at most places provide either high speed screening but generate digital radiography images which are not fully three-dimensionally (3D) volumetric, or provide relatively detailed 3D volumetric images using computed tomography (CT) at a slow screening speed.
Recently developed screening systems such as the real-time tomography (RTT) screening system developed by Rapiscan Systems, Inc. can screen items such as luggage at a very high rate and produce high-resolution 3D volumetric images. FIG. 1a illustrates the RTT screening system. A piece of luggage 102 is passed through the RTT screening system 100 and a 3D volumetric X-ray image of the luggage 102 is displayed on the monitor 104. FIG. 1b illustrates the 3D volumetric image 105 of the piece of luggage 102 screened by the RTT screening system 100.
The RTT screening system 100 comprises a stationary gantry CT design that controls a plurality of X-ray emitters. It captures 3D images at several times the speed of legacy CT systems. FIG. 2 is a block diagram illustrating high level data flow in the RTT screening system. The RTT screening system 202 comprises a reconstruction engine 204 which receives sinogram data from RTT hardware 202, and produces a high resolution 3D reconstructed image. A threat detection engine 206 receives the reconstructed image as an input from the reconstruction engine 204 and processes it by applying one or more automatic threat detection algorithms to generate a decision, e.g. all clear or signal an alarm, on the image. The threat detection engine 206 then passes on the data comprising the image and the result of processing of the image to a storage device 208, where it is stored temporarily. The same data is retrieved by the 2D and 3D operator workstation(s) 210, 212 and specifically assigned to alarm resolution stations 214 over a network, such as an Ethernet. Regulatory authorities may require high security regions such as airports to store the image data for a predefined period of time, i.e. up to 48 hours. The data is then written to a disk storage system 216 for long term storage, and passed to various display workstations in real-time. U.S. patent application Ser. Nos. 10/554,656, 10/554,975, 10/554,655, 10/554,570, 12/097,422, 12/142,005, and 12/787,878 disclose various aspects of the RTT system and their specifications are incorporated herein by reference in their entirety.
The high-speed RTT system can generate a data rate as high as 400 MB/sec. The data is required to be stored for later retrieval, and also accessed by the 2D and 3D workstations 210, 212 as quickly as possible. Commercially available standard network attached storage (NAS) devices typically store data on an array of hard disk drives. Typically, standard NAS consists of redundant array of inexpensive disks (RAID) to ensure high levels of data integrity. The purpose of the storage array is to store various bag files (.BAG) scanned by the RTT system 202. The storage array also stores engineering/intermediate data such as information associated with the bag images, system calibration information, system configuration, event logs, among other information.
Due to file system overhead and read/write seek time of the hard drive sub-system, among other reasons, standard NAS devices cannot effectively simultaneously store the data at high speed and also provide sustained high-speed read access to multiple screener workstations. Typical hard disk arrays have a seek time of about 15 ms. Therefore, when a standard NAS device tries reading and writing at the same time, the hard drive ends up spending most of the time seeking, thus reducing the effective throughput.
Hence, there is need for a NAS device which provides a high speed temporary storage system that stores high resolution image data and associated detection results. There is also a need for a NAS device that can concurrently or simultaneously store data at high speed and also provide sustained high-speed read access from multiple screener workstations.